This invention relates to apparatus for binding documents in a polyethylene cover having a heat reactivatable adhesive secured to the inside linear portion of the backbone thereof.
The general subject matter of this case insofar at least as it deals with binding covers having a heat reactivatable adhesive secured to the backbone or spine thereof is related to co-pending applications U.S. Ser. No. 265,305, U.S. Ser. No. 371,550, U.S. Ser. No. 468,133, U.S. Ser. No. 452,621 and U.S. Ser. No. 452,622, all assigned to the same assignee as this application.
In the original adhesive cover concept, conventional paper covers were used which have heat reactivatable adhesive secured to the inside backbone portion of the cover. The process of making these covers is implemented by placing the external backbone portion of the cover against a hot oscillating heater. Normally, temperatures in the 300.degree. - 350.degree.F range are used as the heater temperature. This elevated temperature range yields reasonably fast processing and is adequate in that it is not so hot as to scorch or otherwise damage paper or ink on the external backbone of the cover.
During the development of the adhesive cover concept it became desirable to use linear polyethylene for covers instead of conventional paper of card stock. The advantages of linear polyethylene include low cost, good hinging properties, ruggedness, long life, and excellent aesthetics. While these properties are most desirable in the linear polyethylene cover, other problems are created in its use. For example, in the process of reactivating the adhesive attached to the inside of the backbone, the exterior surface of the linear polyethylene cover is often subject to melting and/or distortion. In other words, the linear polyethylene melts quite readily when placed in contact with a heater of the type mentioned above which operates in the 300.degree. - 350.degree.F range and it does so before reactivation of the adhesive occurs. If the heater temperature is decreased to accommodate the linear polyethylene the process time is increased to a point where it is no longer commercially desirable. Adhesives with lower heat susceptibility also have been proposed, but to do this would increase the susceptibility of the book to self-destruction under high ambient temperatures. Other plastic sheet materials which might have a higher heat distortion point do not permit the introduction of a useful hinge with a significant commercial life.
Accordingly, it has become desirable to develop some other means of reactivating the adhesive if the linear polyethylene cover material is to be used and the above problems avoided.